1. Field of the Invention
The invention relates refinement in an abnormality detecting device for detecting an abnormality which has occurred in a vehicular hydraulic pressure control circuit.
2. Description of the Related Art
Generally, an automatic transmission for a vehicle is controlled by engaging/applying or disengaging/releasing a plurality of hydraulic friction engaging devices included in the automatic transmission, using operating oil which is supplied from a predetermined hydraulic pressure control circuit. In recent years, an automatic transmission, in which each of the plurality of the hydraulic friction engaging devices is controlled by a dedicated electromagnetic control valve, is widely used. With such an automatic transmission, excellent controllability can be obtained. However, when an abnormality occurs in the plurality of the electromagnetic control valves, the automatic transmission might operate irregularly. Therefore, a technology for detecting an abnormality, which has occurred in the plurality of the electromagnetic control valves, is proposed. An example of the above-mentioned technology is applied to a hydraulic pressure control device for an automatic transmission, disclosed in Japanese Patent Laid-Open Publication No. 2003-49937. The hydraulic pressure control device for an automatic transmission includes a hydraulic switch, which detects hydraulic pressure, on the downstream side of a fail-safe valve. Therefore, an abnormality which has occurred in the plurality of the electromagnetic control valves can be detected by a single hydraulic switch.
However, in the conventional technology, when it is determined that the hydraulic switch is ON in the state where the hydraulic pressure should not be supplied, it is impossible to determine whether the hydraulic pressure is output due to an abnormality in the electromagnetic control valve, or there is an abnormality in the hydraulic switch. Namely, under present circumstances, an abnormality detecting device which can reliably detect an abnormality, that has occurred in the vehicular hydraulic pressure control circuit, has yet to be developed.